1. Field of the Invention
The present invention relates to a golf club head, and particular to a groove formed on the face thereof.
2. Description of the Related Art
It is provided on a face of a golf club head plurality of grooves, called marking line, score line or face line grooves. These grooves affect an amount of spin of a ball. In the case of the golf club head of an iron club, especially the wedge, it is desirable to form the grooves in order to increase the amount of spin of a ball.
Japanese Patent Application Laid-Open No. 9-192274 discloses a golf club having grooves of V-shaped or trapezoidal cross section. Japanese Patent Application Laid-Open No. 9-70457 and No. 10-179824 disclose a golf club head having grooves edges (boundary portions between side surfaces of the grooves and a face)of which are rounded. This rounding has an effect of preventing a golf ball from getting damaged (for example, scratches and the like). Japanese Patent Application Laid-Open No. 2003-93560 and No. 2005-287534 disclose a golf club head having grooves each of which has a side surface formed not by a single surface, but by two differently angled surfaces. Incidentally, a golf club head used in official games is subject to constraints on the width and depth of a groove specified by the rules. Therefore, in consideration of applications in official games, it is required to design a golf club head in a range to meet the rules.
Now, an amount of spin of a golf ball in the rain or hitting a shot in the rough tends to be smaller than without the rain or hitting on the fairway. For preventing the amount of spin of a ball in the rain or a shot in the rough from decreasing, it is effective to enlarge a volume of a groove on the face. The enlargement of the volume of the groove allows grass and dust sandwiched between the face and a ball to easily get away into the groove and improves drainage performance of water existing on the face.
A groove having a rectangular cross section can have the largest volume of the groove compared to a groove having the same width and a differently shaped cross section. However, a ball is easily damaged because of an increase in sharpness of the edge of the groove.
On the contrary, a V-shaped or trapezoidal cross section of the groove allows a ball to be less damaged compared to the rectangular cross section. However, the volume of the groove is liable to be small. Therefore, when hitting a shot in the rain or in the rough, the amount of spin of a ball tends to be largely reduced.
In the golf club head disclosed in Japanese Patent Application Laid-Open No. 2003-93560, an enlargement of a volume of groove may increase sharpness of the groove edges, and therefore, a ball may be susceptible to damage. The golf club head disclosed in Japanese Patent Application Laid-Open No. 2005-287534 may be unworkable, because a groove width on the face is narrower than that within the groove. Further, increasing sharpness of the groove edges makes a ball more susceptible to damage. Japanese Patent Application Laid-Open No. 2005-287534 also discloses rounding of the groove edges, however, when the groove edges take an angle as sharp as the grooves of Patent Application Laid-Open No. 2005-287534, a ball may be also likely to suffer damage even if the edges are rounded.